Multimode communication devices are communication devices configured for communication such as radio communication in more than one communication mode. For example, such modes of communication include digital and analog signaling, different frequency bands for communication, and communication according to different communication protocols. Examples of such protocols are Advanced Mobile Telephone Service (AMPS), North American Digital Cellular service according to J-STD-009, PCS IS-136 Based Mobile Station Minimum Performance 1900 MHz Standard and J-STD-010, PCS IS-136 Based Base Station Minimum Performance 1900 MHz Standard ("IS-136"); Code Division Multiple Access (CDMA) radiotelephone service according to EIA/TIA interim standard 95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System ("IS-95"); Global System for Mobile Communication ("GSM"); and satellite protocols such as that proposed by Iridium, L.L.C. ("Iridium;" Iridium.RTM. is a trademark and service mark of Iridium, L.L.C.). A typical communication system provides communication in one of these modes in a limited geographical area. A multimode communication device may use one or more of these modes for communication.
Existing multimode radiotelephones include some cellular telephones. For example, cellular phones according to IS-136 and IS-95 are operable in both an analog mode and a digital mode. Cellular phones according to IS-136 are dual band communication devices in that they operate in a first band of frequencies near 800 MHz and a second band of frequencies around 1900 MHz. Such radiotelephones communicate with a single type of communication system in different modes.
Such previous radiotelephones are constrained by the limited geographic coverage of the system. When the radiotelephone is moved to a new area beyond the system's boundaries, service on the radiotelephone is no longer available. Even though other systems provide service in the new area, unless that service is compatible with the radiotelephone, the radiotelephone can't communicate with the system. Further, service on a system may not be available for a time. Even though other (incompatible) systems provide service to the same area, the radiotelephone is not usable.
A new type of radiotelephone is envisioned which can operate on autonomous communication systems. Autonomous communication systems are communication systems which are independent but may overlap in their geographical coverage areas. Thus, in a particular area, a radiotelephone of this new type may communicate with a terrestrial system such as a GSM system and with a satellite system such as an Iridium system. In a different area, the radiotelephone may communicate with a GSM system and an IS-95 system.
Communication with multiple autonomous communication systems differs from conventional communication with a single system that has multiple modes. In such systems, a mobile station such as a radiotelephone communicates with multiple fixed base stations in the communication system. The base stations, in turn communicate with a network controller or mobile telephone switching office which coordinates the system and provides handoff of communications from base to base and from mode to mode. In autonomous communication systems, the respective systems are autonomous in that there is little or no intercommunication between the two systems. Handoff is not possible between systems. A mobile station for use in multimode communication with autonomous systems must adapt to these limitations.
Moreover, there is a constant desire in the field of communication devices to minimize the product cost of such devices. One common way to reduce product cost is to eliminate duplicate components by re-using a single component in different applications. For example, in dual mode radios according to IS-136 and IS-95, it is known to use a single antenna for both the analog and digital modes of operation. Other shared hardware resources include voltage controlled oscillators and other frequency synthesizer components, digital signal processors and permission to receive and transmit. To be economically viable, future multimode communication devices will need to exploit this concept of shared resources while still being able to communicate with multiple autonomous systems.
Accordingly, there is a need in the art for a multimode communication device and a method for operating such a device which solves these problems.